A number of devices for dispensing measured amounts of materials are known. Reference may be made, for example, to U.S. Pat. Nos. 2,385,677, 2,877,937, 2,898,010, 2,901,150, 3,450,310, 3,695,487, 3,754,688, 4,071,171, 4,429,815, 4,380,307, 4,832,235, 4,957,219, 6,283,339 and 7,959,031. The entire disclosure of each of those patents is incorporated herein by reference for all purposes.